1. Field of the Invention
The present invention relates to a photosensitive polyimide composition; especially relates a photosensitive polyimide composition for flexible printed circuit boards. In addition, the present invention relates to a base agent of the composition and a method of making the base agent. Also, the present invention relates to a solder-resistant polyimide thin film made from the composition.
2. Description of the Prior Art(s)
Although a conventional thin film made from a photosensitive solder-resistant composition having a base agent of epoxy resins is generally applicable to flexible printed circuit boards, the solder resistance, mechanical strength and flame resistance of the thin film cannot meet the needs of high density flexible printed circuit boards.
TWI320514 provides a negative photosensitive polyimide composition. But a high hard bake temperature around 230° C. is needed for the thin film made from the negative photosensitive polyimide composition. In addition, an ethanol solution comprising tetramethylazanium hydroxide (TMAH) serves as the developer for the thin film. Note that TMAH is not a common component of a developer used in the fabrication of printed circuit boards.
TWI265377 provides a negative photosensitive polyimide composition. But a high hard bake temperature around 230° C. is needed for the thin film made from the negative photosensitive polyimide composition. In addition, the thin film is not easy to be developed since the thin film is required to be developed by an ethanol solution comprising TMAH for 90 seconds and then be rinsed by ethanol for 30 seconds. Also, a high exposure energy around 1000 milli-joule per centimeter square (mj/cm2) is needed for the thin film. Further, the dielectric constant and dielectric loss of the thin film is high after being developed; thereby the thin film cannot meet the needs of high density flexible printed circuit boards.
TWI374158 provides a photosensitive polyimide. Although shown to be a photosensitive polyimide, TWI374158 does not mention any relevant electrical property, thermal resistance, flexibility and chemical resistance, etc. Based on the specification of TWI374158, the photosensitive polyimide shall be a film. In this way, the photosensitive polyimide is needed to be laminated on a printed circuit board by an attaching machine, thereby causing poor sealing and storage stability problems.
Accordingly, conventional technique does not provide a photosensitive composition that can fabricate a thin film; a thin film has low hard bake temperature and low exposure energy and can be developed by a weak alkaline developer. In addition, the conventional developed thin film has high dielectric constant, high dielectric loss, weak flame resistance, weak solder resistance, and weak mechanical properties. Therefore, the conventional photosensitive composition and the thin film made from that do not meet the needs of high density flexible printed circuit boards.
To overcome the shortcomings, the present invention provides a photosensitive polyimide composition, a base agent of the photosensitive polyimide composition, a method for making the base agent, and a solder-resistant polyimide thin film made from the photosensitive polyimide composition to mitigate or obviate the aforementioned problems.